This invention relates to improved gas-liquid contact apparatus for fractionation towers or other vessels which have beds of packing formed of stacked grids.
Packing materials are used in chemical processing apparatus to provide passage for upwardly flowing gases and to provide supporting surfaces for downwardly flowing liquid. Liquid introduced to the upper end of the packing flows downwardly as a thin film on the surfaces of the packing material. Gaseous vapors are injected into the lower end of the vessel and ascend through the openings in the packing material, moving through the vessel in intimate contact with the liquid film on the surfaces of the packing. Such contact between the liquid and gas can produce mass transfer, a chemical reaction, heat exchange and/or scrubbing of the gaseous stream.
The invention described in this specification is primarily envisioned for use in pump-around sections and flash sections of vacuum fractionating towers where direct contact between the vapor and the liquid is used to remove heat from the ascending vapor. In flash sections, there is a low liquid flow rate in relation to the gas flow rate. Ideally, there is a minimal amount of entrainment of liquid droplets into the gaseous stream, a minimal pressure differential between the incoming gases and the outgoing gases, and a continuous downward flow of liquid which assures that effective heat exchange will continue throughout a wide range of gas flow rates.
Many fractionating towers are equipped with grids, known in the art as Glitsch Grid, which are similar to the grids shown in FIGS. 1 and 18 of Winn et al., U.S. Pat. No. 3,343,821. Grids constructed according to the present invention are believed to provide a lower pressure drop and a similar efficiency to the Glitsch Grid. Furthermore, the improved grids are less complicated and less expensive to manufacture and install than the Glitsch Grid. The grids disclosed in this specification can be made of larger and fewer parts, and they can be assembled with little or no welding. They are also more rigid which reduces the need for supporting truss structures and simplifies the task of removing the grids from towers in situations where replacement is required.
The principal objective of the present invention is to provide a packing with low pressure drop, reasonable efficiency and minimal entrainment at high gas flow rates. Additional objectives are to provide a packing which is relatively uncomplicated, easily manufactured and structurally sound.
With regard to its physical configuration, the present invention involves several improvements to the type of grid illustrated in FIGS. 5 and 12 of the Winn et al. U.S. Pat. No. 3,343,821. As will be described in greater detail below, these improvements pertain to the manner in which the flanged grid members are connected together, the presence of openings in the flanges of the grid members, a modified orientation of the flange segments to reduce the constriction to the flow of ascending gas, and the provision of interruption means which are located in the webs below the ends of the flange segments in order to provide longitudinal distribution of the liquid on the webs. The invention also relates to an improved method of manufacturing the grid to reduce fabrication and assembly costs.